Fighting glaucoma with neuroprotective agents

February 1, 2012

A pharmacoeconomic argument for neuroprotective agents is discussed

Glaucoma is a chronic, degenerative optic neuropathy characterized by the progressive thinning of the neuroretinal rim of the optic nerve, resulting in the enlargement of the opticnerve cup. Its cause is the loss of retinal ganglion cell axons, along with supporting glia and vasculature.

Glaucoma has been nicknamed the 'silent thief of sight' because the loss of vision normally occurs gradually over a long period of time and is often only recognized when the disease is quite advanced. Once lost, this damaged visual field cannot be recovered. Worldwide, it is the second leading cause of blindness affecting 1 in 200 people aged 50 and younger, and 1 in 10 over the age of 80.

Myogane* is a neuroprotectant that has been demonstrated to prevent retinal ganglion cell death in culture - a model of glaucoma in vitro and is currently in development by Phytopharm plc as a potential treatment for glaucoma. In glaucoma, the ganglion-cell axons that make up the optic nerve are damaged by a variety of factors, only some of which are understood.

The most important risk factor for glaucoma is elevated intraocular pressure (IOP) which is believed to provoke the neurodegeneration in susceptible subjects. However, even though elevated IOP is a significant risk factor, the majority of patients diagnosed with glaucoma have an IOP in the normal range.

The opticnerve damage in glaucoma is not yet amenable to direct treatment, consequently intervention is currently focused on the only known risk factor that can be modified, elevated IOP. Reduction in this is associated with a significant reduction in the rate of progression with the benefits of treatment being observed after 6 months of treatment.

However, glaucoma is a chronic condition and more than half of patients will demonstrate disease progression within 8–10 years of diagnosis despite efforts to reduce IOP. Poor compliance with medications is a major reason for vision loss in glaucoma patients.

A 2003 study found that half of patients in a health maintenance organization never filled their initial prescription for eye drops and another survey found that one in four patients failed to refill their prescriptions a second time, even though eye drops need to be used every day to be effective. Patient education and communication must be ongoing to sustain successful treatment plans for this lifelong disease with no early symptoms.

For these reasons, there is considerable interest in the development of oral drugs that may provide neuroprotection and thereby reduce the rate of glaucoma progression.